The present invention generally concerns an instrument for measuring the tension of yarns--particularly weft yarns which wind or unwind forming a "balloon"--in any yarn treatment operation in the weaving and spinning fields and, specifically, in weft yarn feeding to looms by means of weft feeders.
The invention also concerns a weft feeder equipped with an instrument of the type specified heretofore.
The main and more general object of the invention is to measure the tension of a yarn without forcing it to undergo further deviations--as it happens at present with the conventional devices--when a "balloon" is formed due to yarn operating conditions, but taking instead advantage of the vertex of the "balloon" both in the "defile" unwinding of the yarn (as at the outlet of a loom weft feeder) and in the winding thereof (as at the inlet of a spinner).
A further object of the invention is to improve weft yarn feeding to looms by making use of weft feeders to which there is associated an instrument for measuring yarn tension in the aforementioned way, and using the data of the measurements carried out with the instrument in order to influence the treatment operations to which the weft yarn being fed is subjected.
Considering in particular the case of loom feeding, it has to be taken into account that--as known--the efficiency of modern looms is highly influenced, in terms both of quantity and of quality of the product, by the tension of the weft yarn with which they are fed. This tension does not only depend on the type and characteristics of the yarn and on the kind of weaving being performed, but also on a large number of other parameters subjected to variations which are difficult to quantify. These variations may be, due to differences in the features of the yarn reels, both in each reel and between one reel and the next (even forming part of a same lot), or to the change of environmental conditions, to the ageing of the parts of the weaving system, and so on. Furthermore, the adjustments of the brake members are carried out nowadays in a qualitative way, leaving the delicate task of the most appropriate choices to the sensitiveness and experience of the operator, which are not always adequate.
Hence, it appears of utmost interest to be able to obtain a quantitative information on the braking conditions of the weft yarns fed to a loom, in the form of numerical indications of the tension expressed in units of absolute or relative force onto a suitable visualizer, and to use this information so as to automatically and continuously adjust the brake members in order to guarantee the constancy of the tension in the long run.
This is very efficiently obtained with the tension measuring instrument proposed by the present invention which, as already mentioned, by no means modifies--as it negatively occurs instead with the devices adopted up to date--the normal yarn feeding path from the weft feeder to the loom.